Thrust reversers on large jet engines on aircraft are typically formed of individual cascade baskets circumferentially positioned aft of the engine adjacent the jet exhaust nozzle. The present cascade baskets are in the form of cast aluminum or magnesium or made in dies or molds which are extremely sophisticated. In a typical engine there are ten or twelve types of cascade baskets, requiring the same number of molds for a typical engine. These molds are extremely expensive each ranging in price from between $200,000 and $300,000. Such costs obviously substantially increase the price of airplanes.
Therefore, attempts have been made to make the cascades and molds in different ways and from different materials. Earlier and current attempts to utilize injection molds have failed because of the inherently low structural characteristics of the selected molding material, for example, glass or graphite reinforced nylon.
One technique developed a complete cascade from an injected mold die. This was a completely reinforced nylon unit. Air loads and sonic fatigue immediately destroyed this unit under test and quickly confirmed that nylon could not handle main strongback loads. In addition, this test unit also permitted an assessment of knit lines (inherent material weld lines or flow gating fronts) and illustrated their deficiency in structurally designed items.
For understanding, each unique vane must carry airloads, individually and beam such airloads to its side members, the strongbacks, which in turn beam load forward and aft to the cascade structural attachment flanges. The strongbacks collect all vane loading and consequently become the workhorse for the cascade load carrying capability. Strongbacks, designed practically with respect to attaining maximum flow area, that is, minimum width, cannot react the vane loading when degraded by the low structural material allowables associated with reinforced nylon and the impact of knit lines, or weak or deficient junctions within.
It appears, that a completely die injected molded part cannot be designed within the current envelope of minimum space and weight and be competitive with cast magnesium or aluminum cascades without a major breakthrough in terms of a new high-strength molding material.
Another technique recognized the inherent low structural properties of reinforced nylon, especially when used for strongbacks, and attacked the problem accordingly. This cascade was fabricated by molding separate nylon vane ladders and mechanically fastening these individual ladders into a fore and aft skeletal frame made of a stronger material, i.e., cast aluminum. In effect, the failure of strongbacks to handle successive vane loads was overcome by simply providing a high strength backbone of material that could support the induced loads.
The deficiency of this design was the poor performance aspect, namely, loss of flow area, due to having to mechanically fasten nylon strongbacks to skeletal strongbacks. The overall basket was only as good as the mechanical joint which was awkward, heavy, and bulky. For such a design, a massive flow area envelope must be available to operate successfully. This concept was not conducive to minimum reverser weight but was just the opposite.
A search of the patent literature discloses various types of items including vanes which are provided with internal metal reinforcement and are covered with an outer non-metallic material. Cascade fabrication relating to the present invention was not found.
The following patents were found in the search.
U.S. Pat. No. 2,120,277 PA0 U.S. Pat. No. 2,929,755 PA0 U.S. Pat. No. 2,946,104 PA0 U.S. Pat. No. 3,248,082 PA0 U.S. Pat. No. 3,318,388 PA0 U.S. Pat. No. 3,647,317 PA0 U.S. Pat. No. 3,832,264 PA0 U.S. Pat. No. 3,914,368 PA0 U.S. Pat. No. 3,972,974 PA0 U.S. Pat. No. 4,100,248 PA0 U.S. Pat. No. 4,351,786